Keshavamurty, R. N., 1982: Response of the atmosphere to sea surface temperature anomalies over the equatorial Pacific and the teleconnections
of the Southern Oscillation. Journal of the Atmospheric Sciences, 39 (6), 1241-1259.
Abstract: In order to improve our understanding of the role of equatorial Pacific
sea surface temperature (SST) anomalies in the Southern Oscillation and
the variability of the Walker Circulation, we have conducted sensitivity
studies with warm SSTA's over different parts of the equatorial Pacific
using a general circulation model of GFDL. The model response is compared
with the variability of the 15-year control run and the statistical significance
of the response is assessed.
The anomalies produce dominant changes in the vertical circulation in the
equatorial longitude-height plane. Besides the large local increase of precipitation
near the anomalies and a slight reduction to the west, there are also global-scale
anomalies in the equatorial zonal winds (notably in the upper troposphere)
and in tropical sea level pressure. The Pacific Walker Circulation is significantly
altered. In the case of eastern and central Pacific anomalies these features
resemble the observed circulation anomalies during the low index phase of
the Southern Oscillation. Thus warm SST anomalies over equatorial eastern
and central Pacific are shown to act in such a way as to reinforce the low
index phase of the Southern Oscillation. The model response of the low-level
zonal winds is such that the maximum westerly anomalies occur to the west
of the SST anomaly. This would induce the anomalies to shift westwards.
We also propose a self-generating mechanism for the Southern Oscillation.
SST anomalies over equatorial central and western Pacific are found to
be more efficient in producing atmospheric circulation anomalies compared
to equal ones over eastern Pacific. The details of the response are also
longitude dependent.
The anomalies also produce well-marked subtropical and middle latitude
responses, notably in the winter hemisphere. The subtropical anticyclones
and the subtropical westerly jet streams in the upper troposphere are strengthened
in the longitudes of the anomalies whereas the westerlies in the subpolar
latitudes are weakened. In other longitudes there is a weakening of the
subtropical anticyclones. The precipitation also increases southeastward
and northeastward from the anomaly. There is also a stationary anomaly low
(in the middle latitudes) to the southeast of the SST anomaly and an anomaly
high further southeast.
The diabatic heating anomalies associated with the central and western
Pacific anomalies induce circulation changes over south Asia similar to
those observed during drought years.
The central Pacific anomaly also produces westerly anomalies in the tropical
stratosphere, around the globe.